Our gray three-ring plastic binder mechanisms come in a 1" round ring size. Plastic binder spines are sized for standard letter size 8 ½" x 11" paper and feature two boosters to allow for easy ring opening and closing. With traditional 4 ¼" spacing between these rings, they can be used with any standard US three hole punched paper. Although made primarily of a thick, durable resin plastic, the backing of these ring binder parts is made of metal for added stability and strength. Plastic binder spines offer a unique alternative to traditional metal spines.